As conventional methods for joining a metallic material and a resin material, a method using rivet fastening and a method using adhesives are exemplified. Rivet fastening is a physical fastening method comprising knocking a rivet having a diameter of several millimeters to several tens of millimeters into a metallic material and a resin material in a state wherein they are superposed each other so as to penetrate the materials to fix the materials. On the other hand, adhesion is a method comprising fixing a metallic material and a resin material by physical adsorption force and chemical adsorption force via an adhesive.
For joining using laser, a method for joining metallic materials or resin materials by welding and deposition is practically used, but joining between a metallic material and a resin material has not been effected yet. However, in recent years, in laser resin joining, an innovative method for joining by superposing a material being transparent relative to the wavelength of laser light and a material being opaque relative to the wavelength of laser light each other, and irradiating the materials with laser light from the side of the transparent material so that only the portion to be joined is melted, has been put into practical use. In this method, a large joint area can be obtained and generation of gas due to decomposition of the resin during heating can be suppressed [see Japanese Patent Application Laid-open (JP-A) No. 2003-325710, JP-A-60-214931, JP-A-2002-67165, and Proceedings of the 59th Laser Materials Processing Conference, pp. 1-7 (September 2003)].
There is a very strong demand for joining a metallic material and a resin material. This is because, by using a metallic material only in a desired portion and replacing the residual portion with a resin material, various merits can be obtained: the weight and cost can be largely reduced because a resin material weighs and costs not more than half that of a metallic material; freedom of designing with regard to excellent electric and heat characteristics due to insulator resin materials is improved; or that a novel composite functional material is produced by combining them.
However, the field of application is limited under the current situation in the method using rivet fastening or an adhesive, which is a conventional method for joining a metallic material and a resin material. Rivet fastening is mainly applied to large or simple commercial products or parts because the fastening portion has a considerable size and weight and the size and weight of parts are necessarily increased and the freedom of designing is decreased. On the other hand, in adhesion, the size and weight are not increased, but there are technical problems that precise pinpoint joining is difficult because the adhesive is wet and extended, that the surface to be adhered is restricted, for example, adhesive strength on an uneven surface is higher than that on a plane surface, and that production tact is decreased due to long cure time and maintenance and control of the state of the adhesive are difficult during production. In the joining using laser, selection of materials is limited since a resin material being transparent relative to the laser wavelength and a resin material being opaque relative to the laser wavelength must be used as in the joining of resins, and there is a problem in manufactural technology that laser irradiation can be effected only from the transparent resin material side. The same problems also exist in joining of a glass material and a resin material and joining of a ceramic material and a resin material.